You execute the following commands: SQL > DEFINE hiredate = `01-APR-2011` SQL >SELECT employee_id, first_name, salary FROM employees - WHERE hire_date > `&hiredate` AND manager_id > &mgr_id; For which substitution variables are you prompted for the input? 

Answer options:

A. none, because no input required
B. both the substitution variables ``hiredate` and `mgr_id`.
C. only hiredate`
D. only `mgr_id`

D